"We have been on a challenging mission," Grunsfeld said. "Hubble isn't just a satellite. It's about mankind's quest for knowledge. The only way to find the limits of the possible is to go beyond the impossible. Many people said we could not do this. We have achieved this and we wish Hubble the very best."

His partner Feustel also had some final words.

"I'm just really proud to have been a part of this," he said, thanking his wife, children, crewmates and NASA colleagues on the ground.

Cmd. Scott Altman congratulated his crew, saying, "The sign of a great crew is that the commander doesn't have a lot to do. I appreciate all of the work we've had together. … It's been a great thrill. I'm very proud of the crew and the whole team."

NASA: 'Hubble's Never Had it Better'

Feustel and Grunsfeld started work this morning an hour early. During the spacewalk, the duo installed a new set of batteries, a Fine Guidance Sensor that helps aim the telescope and protective steel-foil sheets on the telescope's exterior.

As they worked, the crew appeared to be in good spirits.

"Rollin', rollin', rollin," astronaut Mike Good sang from inside the cabin, as Grunsfeld used a roller to help the steel blanket stick to the telescope's exterior.

Before the astronauts could re-enter the shuttle, they had to thoroughly clean off the debris from their gloves. Specialists on the ground were concerned that gold foil sticking to Grunsfeld's gloves (from when he removed old insulation) would contaminate the shuttle's interior.

As the astronauts were preparing to re-enter the shuttle, Grunsfeld's backpack bumped into an antenna. Mission Control sent them back to re-adjust the end cap of the antenna to make sure it was working. Once they were sure that antenna was in good shape, the astronauts and specialists on the ground gave their last remarks.

"Hubble's never had it better. It's never been more capable," spacecraft communicator Dan Burbank said. "It's just been a marvel to watch you guys do this."

Thanks to the astronauts repairs, the telescope should be able to photograph the cosmos for another five or more years. NASA expects to launch the more advanced James Webb Space Telescope in 2014. When Hubble retires, this new telescope will pick up from where it left off.

The astronauts will release the Hubble Space Telescope Tuesday and, after additional tests and preparations, are scheduled to return on Friday.

Scientists Will Know Outcome of the Repair Mission in Three Months

It will be three months before scientists know how well all of the new instruments work. The Goddard Space Flight Center in Maryland will unveil the new discoveries after Hubble's renovation Sept 7. In total, this Hubble mission costs more than $1 billion.

"We fought against tremendous odds to fly this mission, and we succeeded beyond our wildest dreams,"said Chief Hubble Scientist Dave Leckrone, after the spacewalk was over.

On Sunday, Astronauts Mike Massimino and Good were tasked with installing the steel New Outer Blanket Layer Sunday, but were unable to accomplish it because the spacewalk fell three hours behind.